CS(AR)-25/97-98 : Conjunctive use studies in Pennar delta canal system: Aquifer response modelling for Southern channel command area

Abstract

In a hydrological system surface water flows, low or high, does not necessarily coincide with the low or high levels in groundwater, because of the sluggishness of the groundwater flow compared to surface water flow. Also excessive development of groundwater in the deltas and coastal areas may lead to salt water ingress into the freshwater aquifer and may contaminate it, if unchecked. This may happen when sufficient surface water supplies do not reach the tail ends of command areas.

With the increasing knowledge of the hydrogeological features of potential aquifers being identified with latest geophysical investigations, the scope for better conjunctive use practices are very good. The prospects of practicing conjunctive use of surface and groundwater will be better provided one understands the hydro-climatology of the study area along with hydrogeology of the region. Collaboration between different government authorities and non-governmental organisations, is also essential. As a farmer switches over to using groundwater when there is frequent shortage of dependable surface water supplies the practice of conjunctive use is user-friendly natural resort as far as practicing is considered. Hence cultivators will be accommodative to suggestions on conjunctive use provided maximum benefit is assured.

A study on aquifer response modelling was undertaken for the Southern Channel command area (118 sq. km.) in the Pennar delta canal system in Andhra Pradesh to understand the potential or the dependability of groundwater supplies in the study area so that limited surface waters can be supplied to other much deserved areas.

The conjunctive use modelling at seasonal level, i.e., for water supply under canals during monsoon season and under wells during non-monsoon season is studied as a lumped model based on the water balance studies undertaken earlier for the study area. An attempt is made to simulate the drawdown due to pumping of ground water around a single well. Finally top aquifer is simulated using a finite difference method at a grid level of 1 km X 1km. Pumping at different nodes is derived based on the number of filter points and extent of geographical area served by the village falling with in the grid. The aquifer parameters are adopted as those used for water balance study.